BezierCurve extrudes too much
I think it's just your Handle Type. 

If the Handle Type is'Free' or 'Aligned', the default behavior of E extrude is to copy the source vertex, along with its control points. If the control points are extended, that will also create a segment of some length. If the extrusion is from a 'Vector' or 'Automatic' (unadjusted) vertex, the system has the opportunity to adjust the front-facing handle of the previous vertex, as you extend the curve.